Gigabit COTS Ethernet Switch Evaluation for Avionics - CiteSeerX

Gigabit COTS Ethernet Switch Evaluation for Avionics a

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J. Meier , S. Kim , A. George , and S. Oral Rockwell Collins Adv. Tech. Center, ACS Department, Cedar Rapids, IA HCS Research Lab, ECE Dept., University of Florida, Gainesville, FL {jlmeier,sjkim}@rockwellcollins.com, {george,oral}@hcs.ufl.edu

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performance with decreasing costs for a wide array of applications. In this paper, we summarize our evaluation of three commercial switches (Extreme Networks Summit1i switch, the Cisco Systems Catalyst 6500 switch, and the Nortel Networks PassPort 8100 switch), using standard procedures [2-5] to meet flight-critical system requirements.

Abstract The evolving network needs of both commercial and military aircraft are expanding the requirements from slow speeds (1 Mbps) to over 1 Gbps for many new aircraft designs driven primarily by advanced video technology. Low-cost Ethernet switch technology is a key enabler for advanced aircraft system interconnection. Our research focuses on the evaluation of several Gigabit Ethernet (GE) COTS switches to meet avionic requirements. The results indicate that GE COTS switches are beginning to approach the required performance for future avionic applications.

2. Avionic Requirements Key avionic switch requirements evaluated for future commercial and military networks included non-blocking architecture, line-rate capacity, bounded latency, bounded jitter, guaranteed bandwidth for each traffic group, multiple priority levels for each traffic group, maximum frame-size setting for each traffic group, and other related metrics. First, a top-level review of the key requirements was completed. The next step measured several key switch performance parameters (latency, jitter, QoS) to determine suitability for insertion into a flight-critical system. In the past, the latency and jitter of COTS Ethernet switches varied widely, dependent upon loading conditions, making them unsuitable for deterministic avionic system solutions. Our experiments indicate that GE technology shows improved latency, jitter, and related QoS performance.

1. Introduction Cockpit and cabin avionic networks are driving higher bandwidth to handle larger amounts of data. Certification requirements for avionic systems in the cabin (typically Level E) are much easier to meet than most cockpit (Level A) flight-critical applications. Switched Ethernet is a highly standardized (IEEE 802.1D) technology that is designed to meet commercial network needs, however little or no consideration is given to meeting flight-critical avionic requirements with the exception of ARINC 664. Thus, our research evaluates the avionic network performance concerns regarding loading, latency, jitter, and packet loss relative to using COTS Gigabit Ethernet technology for flight-critical applications. Rockwell Collins and the University of Florida conducted experiments with three of the leading GE switches to determine their potential suitability for avionic applications, paying particular attention to QoS performance. Different queuing schemes and scheduling algorithms significantly affect the switch scalability for achieving desired QoS performance [1]. New and emerging switch architectures and protocols leverage these new QoS features for high-speed networks, such as Gigabit Ethernet, and promise increasing levels of

2.1. Latency Switch latency is a key performance parameter since flight-critical data must be delivered on time. Switch latency is defined as the duration of time it takes for a frame to pass through a switch. Figure 1 indicates the latency measured verses packet sizes (64, 512, and 1518 bytes) at various loading levels. The lowest latency (4.2µs) for reduced loading conditions greatly surpassed the avionic requirement needs. The 512-byte packet size in the Summit1i had much better performance at near line-rate than either the 64- or 1518-byte packet sizes, as shown in the figure. The Catalyst 6500 latency increased for larger

1 Proceedings of the 27th Annual IEEE Conference on Local Computer Networks (LCN’02) 0742-1303/02 $17.00 © 2002 IEEE

packet sizes but remained relatively (predictable) as loading increased.

through layer-4 fields, with many additional monitoring and management features. Overall, our results show that the Summit1i switch was capable of regulating minimum bandwidth fairly well, albeit not quite as well for very small frames (10% deviation). This limitation is more of an issue in avionic systems, where smaller frames are typically used for flight-critical applications. Priority-based QoS is deemed less important to avionic applications because the switch algorithms are unable to be modified. In such a case, it is difficult to predict the bandwidth affects due to non-standardized control algorithms.

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3. Conclusions

Figure 1: Summit1i Latency Results

The three Gigabit Ethernet switches evaluated all were found to possess widely different capabilities, with the Catalyst 6500 being the closest to meeting the avionic system performance needs. The Catalyst 6500 switch latency stayed virtually constant with increased loading, jitter performance was excellent (within 300ns), and it provided adequate bandwidth allocation control via flexible, smaller bandwidth allocation settings. Overall, the bandwidth allocation results indicate promise for using GE COTS switches in avionic systems. There are limitations in these commercial switches, such as traffic groups must share QoS profiles rather than permitting a profile for each traffic group, and other similar issues. Future work is needed to analyze more extensive QoS characteristics. New methodologies are needed to better measure the performance of the high-end Ethernet switches and thereby support the development of methods to more easily adapt them for avionic systems.

2.2. Jitter Switch jitter is defined as the variation in switch latencies and often results in real-time performance degradation or additional costs for larger buffers. Figure 2 is an example of our jitter measurements experiments for the Catalyst 6500. As shown in Figure 2, the results show unusual jitter at line-rate loading, indicating 64-byte packets do not follow the trend set for lower loading levels. Worst-case jitter appears to be well within 10µs, and in most cases within a few-hundred nanoseconds, which is adequate for most avionic applications.

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4. References

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Figure 2: Catalyst 6500 Jitter Results

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In addition to control over latency and jitter, mission-critical applications also demand predefined levels of guaranteed bandwidth. New switch features provide traffic groupings by switch ports, MAC and IP addresses, TCP and UDP ports, and other layer-2

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2 Proceedings of the 27th Annual IEEE Conference on Local Computer Networks (LCN’02) 0742-1303/02 $17.00 © 2002 IEEE

G. Nong and M. Hamdi, “On the Provisioning of Quality-of-Service Guarantees for Input Queued Switches”, IEEE Communications, December 2000, Vol. 38, No. 12, pp. 62-69. Paxson, V., Almes, G., Mahdavi, J. and M. Mathis, “Framework for IP Performance Metrics,” RFC 2330, May 1998, (http://www.ietf.org/rfc/rfc2330.txt). Hahed T., "IP QoS Parameters", TF-NGN November 2000. Almes, G., Kalidindi, S., Zekauskas, M., “A One-way Delay Metric for IPPM,” RFC 2679, September 1999, (http://www.ietf.org/rfc/rfc2679.txt). Almes, G., Kalidindi, S., Zekauskas, M., “A One-way Packet Loss Metric for IPPM,” RFC 2680, September 1999, (http://www.ietf.org/rfc/rfc2680.txt).